1. Field of the Invention
The present invention relates to a heat generating resistant element film adapted for constituting an electrothermal converting member as generating means for discharging thermal energy for an ink jet apparatus, which discharges ink by an ink jet method for recording or printing a character, a symbol, or an image onto a recording medium constituted of a paper, a plastic sheet, a cloth or another article, an ink jet head substrate and an ink jet apparatus utilizing an electrothermal converting member utilizing such heat generating resistant element film, and a producing method therefor.
2. Related Background Art
An ink jet apparatus has a configuration for discharging a functional liquid for recording etc. (hereinafter representatively called “ink”) from a discharge port onto a recording medium thereby executing a recording of a character, a symbol, an image etc., or an application of a component contained in the ink onto various surfaces, and has a feature capable of a high-speed recording of a high-definition image by discharging the ink as a small liquid droplet from the discharge port at a high speed. In particular, an ink jet apparatus of a type utilizing an electrothermal converting member as energy generation means for generating an energy to be utilized for ink discharge, and executing the ink discharge utilizing a bubble generation in the ink by the thermal energy generated by such electrothermal converting member, is recently attracting attention as it is adapted for achieving a higher definition in the image, a higher speed in recording, a compactization of a recording head and an apparatus, and a color capability (for example, U.S. Pat. No. 4,723,129 and U.S. Pat. No. 4,740,796.
A general configuration of a principal part of a heat substrate to be used in constructing an ink jet apparatus is shown in FIG. 1. FIG. 2 is a schematic cross-sectional view of a substrate 2000 for an ink jet recording head, along a line 2—2 in a portion corresponding to an ink flow path shown in FIG. 1.
The ink jet recording head shown in FIG. 1 is provided with plural discharge ports 1001, and an electrothermal converting member 1002 for generating thermal energy to be utilized for discharging ink from each discharge port is provided for each ink flow path 1003 on a substrate 1004. The electrothermal converting member 1002 is at least constituted of a heat generating resistant element 1005, and a pair of electrodes 1006 connected thereto for an electric power supply thereto, and, in the apparatus shown in FIG. 1, there is provided an insulation film 1007 as a protective layer for at least covering a portion constituting a heat action surface to the ink in the upper part of the heat generating resistant element 1005.
Also each ink flow path 1003 is formed by adjoining a top plate integrally bearing plural flow path walls 1008 under a relative alignment with the electrothermal converting members etc., on the substrate 1004, for example, by image processing. Each ink flow path 1003 communicates, at an end opposite to the discharge port 1001 thereof, with a common liquid chamber 1009, which stores ink supplied from an ink tank. (not shown).
The ink supplied to the common liquid chamber 1009 is guided therefrom to each ink flow path 1003, and is retained therein by forming a meniscus in the vicinity of the discharge port 1001. In this state, the electrothermal converting element 1002 is selectively driven to cause rapid heating and boiling, by the thermal energy generated therein, of the ink on the heat action surface, thereby discharging the ink by an impact force in such situation.
As shown in FIG. 2, a substrate portion in the ink jet head is provided, on a silicon substrate 2001, with a structure of a heat accumulation layer 2002 constituted of a thermal oxidation film on the surface of the silicon substrate, an interlayer film 2003 constituted of an SiO film or an SiN film and having also a heat accumulating function, a heat generating resistant element layer 2004, a metal wiring 2005 constituted of an electrode layer of a metal or an alloy such as Al, Al—Si, Al—Cu etc., a protective layer 2006 constituted of a SiO film, a SiN film etc., and an anticavitation film 2007, laminated in this order. The anticavitation film 2007 is provided for protecting the protective film 2006 from chemical and physical impacts resulting from the heat generation of the heat generating resistant element layer 2004, and forms a heat action portion 2008 in a part contacting with the ink. The heat generating resistant element 1005 shown in FIG. 1 is formed by exposing a predetermined portion of the heat generating resistant element layer 2004 between the electrode layers 2005.
The heat generating resistant element to be employed in the recording head of the ink jet apparatus having the aforementioned structure is generally different from the heat generating resistant element employed in a thermal print head.
This is because, in a thermal print head, an electric power of about 1 W within a period of 1 msec is applied to the heat generating resistant element, while, in an ink jet head, an electric power of 3 to 4 W within a period for example of 7 μsec is applied to the heat generating resistant element, in order to gasify the ink within a short time. Since such electric power is several times larger than the electric power applied to the thermal print head, the heat generating resistant element of the ink jet head tends to be subjected to a thermal stress within a shorter time in comparison with that of the thermal print head.
Therefore, in consideration of the discharge and the driving method specific to the ink jet head and different from those in the thermal print head, a matching design (film thickness, heater size, shape etc.) is required for the heat generating resistant element and it is known that the heat generating resistant element employed in the thermal print head is not immediately applicable to the ink jet head.
In the ink jet recording apparatus, a higher functionality such as a higher image quality and a higher recording speed is recently requested increasingly, as explained in the foregoing. Among these requirements, a higher image quality can be achieved by a method of decreasing the size of the heater (heat generating resistant element) thereby reducing a discharge amount per dot and thus reducing the dot size.
Also for achieving a higher recording speed, there can be employed a driving method with a shorter pulse than in the prior drive, thereby increasing the drive frequency.
However, in order to drive the heater with a high frequency in a configuration of a reduced heater size for achieving a higher image quality, it is necessary to increase the sheet resistance.
Now reference is made to FIGS. 3A and 3B for schematically explaining the relationship among various drive conditions as a function of the heater size. FIG. 3A shows a change in a sheet resistance and a current in the heat generating resistant element as a function of a driving pulse width when the heater size is changed from large (A) to small (B) at a constant driving voltage. Also FIG. 3B shows the sheet resistance and the current in the heat generating resistant element as a function of the driving voltage when the heater size is changed at a constant driving pulse width.
As will be apparent from the relationship between the driving conditions and the size of the heat generating resistant element in FIGS. 3A and 3B, it is necessary to increase the sheet resistance in order to employ the same drive conditions as before with a smaller heater size. Also in consideration of the energy, a driving method with an increased sheet resistance and a higher driving voltage reduces a consumed current, thereby decreasing the energy consumption in resistances other than in the heater, thus achieving an energy saving. Such effect becomes particularly conspicuous in a multi-nozzle configuration including a plurality of heat generating resistant elements.
Thus the Japanese Patent Application Laid-Open No. H10-114071 discloses a configuration of constituting a heat generating resistant element of the ink jet head with a thin film of TaxSiyNz with x=20–80 at. %, y=3–25 at. % and z=10–60 at. % thereby enabling a heat generating resistance property of a high resistance adapted for a small dot and realizing an energy saving when applied to an ink jet recording head.
Among the properties required for the heat generating resistant element to be employed in the ink jet head, in addition to a high resistance, a durability is also an important property to be satisfied at the same time.
The resistor in the ink jet head repeats heat generation by a high frequency electric power of short pulses, and a bubble is generated in the ink according to the cycles of the heat generation, thereby discharging the ink. In such state, the heat generating resistant element reaches a temperature of 600 to 700° C., and an eventual change in the resistance of the resistor in such repetition between the room temperature and the high temperature poses a serious problem in the ink discharge.
More specifically, as the ink jet head is generally driven by a constant voltage drive, a trouble is induced in case the resistance shows a large change during the drive.
For example, a decrease in the resistance significantly reduces the service life of the resistor by an excessive current, while an increase in the resistance reduces the current, eventually failing the ink discharge.
It is therefore necessary, as the durability characteristics of the resistor, that the resistor shows a minimal change in resistance even after the temperature hysteresis actually experienced by the resistor. Such durability can be predicted to a certain extent by an evaluation of a temperature coefficient of resistance (TCR characteristics) of the material.
It is known that the durability is generally better when the TCR characteristics of the resistor is very small (ideally zero). In developing a material for the resistor, it is important to simultaneously realize a high resistance and the durability characteristics. The aforementioned patent reference describes that preferable TCR characteristics can be achieved by selecting a specific resistivity at 2,500 μΩ·cm or less.
However, in the recent trend toward the higher image quality, emphasis is given to the substantial elimination of granularity, and, for this purpose, there is desired a discharge amount of the liquid droplet not exceeding 1 pl.
For achieving the ink discharge with a high driving frequency and with multiple nozzles at a discharge amount of 1 pl or less to be requested hereafter, a sheet resistance of 700 Ω/□ or higher is considered necessary, for example, for a drive voltage of 24 V, a pulse width of 1 μs, and a heater size of 17×17 μm in order to suppress a temperature increase in the head and to stabilize the discharge without decreasing the driving voltage.
However, with respect to TaSiN, the aforementioned patent reference discloses to select the specific resistivity of 2,500 μΩ·cm or less in order to obtain preferable TCR characteristics. Stated differently, in case the aforementioned TaSiN is used to attain the recently requested sheet resistance of 700 Ω/□ or higher (corresponding to specific resistivity of 3,000 μΩ·cm or higher), there will result inferior TCR characteristics and an insufficient durability.
Also in case the resistance is elevated in this manner, there also results a difficulty in productivity such as a fluctuation in the specific resistivity.
For this reason, it has become necessary to find a novel material capable of satisfying a higher resistance and a durability. The novel material is also required to be capable of providing a sufficient margin in productivity.
As a material capable of providing the aforementioned sheet resistance, Japanese Patent Publication No. H2-18651, U.S. Pat. No. 4,392,992, U.S. Pat. No. 4,510,178, U.S. Pat. No. 4,591,821 etc., disclose compositions of a CrSiN film. However, these references do not teach nor suggest at all as to which atomic composition of CrSiN film is useful as a heat generating resistant element for the electrothermal converting member of the ink jet head, and a composition capable of also satisfying the durability has not been known at all.